Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/20—Filters
  • G02B5/28—Interference filters
  • G02B5/285—Interference filters comprising deposited thin solid films
  • G02B5/287—Interference filters comprising deposited thin solid films comprising at least one layer of organic material
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
  • G02B5/3016—Polarising elements involving passive liquid crystal elements

Definitions

• the invention pertains to anisotropic multiplayer thin-film coatings and may be used in fabrication of various optical elements, such as polarizers, beam splitters, interference-polarizing light filters, polarizing mirrors, etc.
• the currently utilized polarizers represent polymer films oriented by uniaxial stretching and colored with organic dyes or iodine compounds.
• Polyvinyl alcohol is usually used as the polymer (PVA) in these films [US 5007942].
• Additional layers in such a polarizer for example, a layer of lacquer, perform protective and other functions and are not intended for optimization of transmission of light through the polarizer (or reflection of light - for a reflecting polarizer) from the point of view of light interference.
• polarizer which represents a multilayer structure comprising at least one birefringent layer with the thickness, which provides interference extremum at the exit of the optical polarizer, for at least one linearly polarized component of light.
• This polarizer comprises alternating layers of two transparent (non-absorbing in the working range of wavelengths) polymer materials, one of which is birefringent, and the other - optically isotropic. The birefringence in the polymeric material is obtained via stretching it in one direction by 2-10 times.
• the working principle of such polarizer is in the following: one linearly polarized component of light, to which corresponds the extraordinary (larger) refraction index of the birefringent layer, is significantly reflected from the multilayer optical polarizer due to the difference in the refraction indexes at the boundaries between the isotropic and the anisotropic layers.
• the optical path difference between the wavelengths reflected from the boundaries of layers comprises a whole number of wavelengths, i.e. there is interference maximum.
• reflection of the linearly polarized component of light, to which corresponds the extraordinary (larger) refraction index of the anisotropic layer significantly increases.
• the ordinary (smaller) refraction index of the anisotropic layer is chosen close to the refraction index of the isotropic layer, therefore the other linearly polarized component of the incident light, to which corresponds the ordinary (smaller) refraction index, travels through the multilayer optical polarizer without reflections.
• the polarizer functions as a beam splitter.
• Multilayer polarizer may also contain additional dichroic polarizer (with weak absorbance), axis of which is parallel to the axis of the reflecting polarizer.
• the role of the dichroic polarizer is basically to remove reflections of the external light when such combination polarizer works "in transmission".
• One of the drawbacks of the known multilayer polarizer is the necessity to use large number of alternating layers, due to the low degree of anisotropy (the deference between the ordinary and extraordinary refraction indexes) in the transparent polymer materials. Usually this value does not exceed 0.2. Therefore, coefficient of reflection from the boundaries of layer is small, and to obtain high coefficient of reflection in general one needs 100-600 layers, deposition of which poses difficult technical challenge and requires special precision equipment.
• polarizer comprising at least one anisotropically absorbing layer, at least one refraction index of which increases with the wavelength.
• multilayer polarizer in which the thickness of layers and their refraction indexes are selected such as to provide interference extremum for at least one linearly polarized component of light.
• interference-type polarizer.
• Anomalous dispersion of at least one refraction index of the anisotropic layer allows to effectively polarize light in a wide spectral range.
• Patent [RU 2155978] describes polarizers comprising a film of dichroic organic material, molecules of which or fragments of molecules of which have flat structure and at least a part of the film has crystalline structure.
• such films may be fabricated from various dyes and their mixtures. Crystalline structure of these films allows obtaining high degree of anisotropy and homogeneity of optical characteristics.
• experiments have shown that such films are hygroscopic and require additional protection or processing to modify their chemical properties.
• the already finished films are processed with ions of the 2x and 3x valence metals.
• Optical characteristics of the known films are determined by the order parameter, which in this case is the averaged characteristic, not accounting for the particular situation of the optical axes of the crystalline structure relative to the substrate, which in turn, imposes restrictions on the possibility to obtain structures "film-substrate" with the given optical properties.
• IFP interference-polarizing
• the herein invention is aimed at creating a multilayer optically anisotropic structure, which comprises at least one layer with high degree of anisotropy and perfect structure, while refraction indexes and thicknesses of all layers and their combination is selected according to the known law, according to the purpose of the structure, such as to provide interference extremum for at least one polarization of light.
• the purpose of such multilayer optically anisotropic structure is not limited to only the functions of "traditional polarizers".
• alternating dielectric films with high and low refraction indexes and with the necessary optical thickness (usually equal to or divisible by ⁇ /4), including also at least one optically anisotropic layer, on the surface of the substrate, one may obtain the following main interference coatings for at least one linearly polarized component of light: antireflecting - lowering reflection for the narrow or wide range of the spectrum; mirror-like - increasing reflection of the incident light up to 80-95% and more; interference light filters - extracting spectral regions of various width from the continuous spectrum of the radiation; etc. [Gvozdeva et al., Fisichaskaya optika, M.: Mashinostroenie, 1991].
• the technical result of the herein disclosed invention is the increase of effectiveness of transformation of the incident radiation, according to the functional purpose of the multilayer optically anisotropic structure, due to the reproducible high degree of anisotropy of at least one layer in the structure.
• Selection of the material of the anisotropic layer from the wide spectrum of organic compounds and their mixtures, which form stable lyotropic liquid crystal phase, allows obtaining crystalline layer with certain, predetermined ratio of the main values of axes of the ellipse of the imaginary and real parts of the refraction coefficient.
• Technical result of the invention is also the simultaneous enhancement of durability and shelf life of this structure, while maintaining or reducing its thickness, optimization of the multilayer structure, simplification of its design and method of obtaining due to possibility of selecting materials with the required optical characteristics for separate layers and control of their thickness, as well as manufacturability and ecological safety of at least a part of manufacturing operations.
• the necessary component of the disclosed structure which determines anisotropy of its properties, is the optically anisotropic, at least partially crystalline, layer.
• the initial selection of material for fabrication of such a layer is determined by the presence of developed system of ⁇ -conjugate bonds in the aromatic conjugate cycles, and the presence in molecules groups like amine, phenol, cetonic, etc., situated within the plane of molecules and being a part of the aromatic system of bonds.
• the molecules themselves or their fragments have flat build.
• indanthrone Vat Blue 4
• dibenzoimidazole 1,4,5,8-naphthalenetetracarboxilic acid Vat Red 14
• dibenzoimidazole 3,4,9 10-perylentetracarboxilic acid
• quinacridone Pigment Violet 19
• LC appears as the pre-ordered state of the system, from which through the process of alignment of the supramolecular complexes and subsequent removal of the solvent, the anisotropic crystalline film (or in other words membranous crystal) is created.
• the method of obtaining thin anisotropic crystalline films from colloid systems with supramolecular complexes comprises:
• colloid system should also be thixotropic, for which purpose the colloid system should be at a certain temperature and have certain concentration of the dispersion phase;
• the degree of this influence should be sufficient so that the kinetic units of the colloid system obtain the necessary orientation and form the structure, which will be the basis for the future crystalline lattice of the forming layer;
• the concluding operation is the drying (removal of the solvent), in the process of which the crystalline structure of the layer is formed.
• the planes of molecules are parallel to each other, and molecules form three-dimensional crystal, in at least a part of the layer.
• Optical axis in the crystal will be perpendicular to the planes of molecules.
• Such a layer will possess high degree of anisotropy and high refraction index in at least one direction.
• Optical anisotropy of the said layer is described by ellipses of the imaginary and the real parts of the refraction index, which characterize the angular dependence of the absorption and refraction coefficients, accordingly (the imaginary and the real parts of the anisotropic refraction index).
• the following relationships should simultaneously hold for the components of the imaginary and the real parts of the refraction index of the optically anisotropic layer according to the invention:
• Components of the real and imaginary parts of the anisotropic refraction index, as well as the direction of the axes of the ellipse may be experimentally determined by existing ellipsometry or spectrophotometry methods.
• colloid systems in this case mixed supramolecular complexes will form in solution
• Absorption and refraction in layers obtained from mixtures of colloid solutions may assume various values within the limits determined by the original components.
• Mixing various colloid systems and forming mixed supramolecular complexes is possible due to coincidence of one of the parameters of molecules from different organic compounds (3.4A). Further formation of three-dimensional crystal from a wet layer during drying happens significantly easier.
• Control over the thickness of coating is performed by controlling content of solid matter in the depositing solution.
• Technological parameter in forming such layers will be the concentration of solution, which is conveniently controlled during fabrication.
• the degree of crystallinity of the layer may be controlled with rontgenorgam or with optical methods.
• the said layers are obtained on different substrates using thermal evaporation of the material with its subsequent precipitation on the surface of the substrate; chemical precipitation from solution; cathode dispersion or chemical reaction of the substrate material with a selected material. Besides that, these layers may perform additional functions in the structure, such as protective, smoothing, adhesive and others.
• Figures 1 and 2 schematically present some of the possible variants of directions of dipole moments of the optical transitions of molecules in the crystalline structure of the optically anisotropic layer and the corresponding ellipses of the imaginary and the real parts of the refraction index of the layer.
• Figure 3 presents the multilayer structure according to the disclosed invention, described in the example of embodiment.
• Figures 4 and 5 present spectral dependences of the imaginary and the real parts of the refraction index of the layer included in the multilayer structure.
• Figure 6 presents the spectra of reflection of light from the multilayer structure for the two different directions of polarization.
• Optical anisotropy of the said layer is described by the ellipses of the imaginary and the real parts of the refraction index.
• the main axes of the ellipses of the imaginary and the real parts of the refraction index here are codirectional, but generally directed arbitrarily relative to the coordinate system (Fig. 1), X Y Z associated with the substrate (or the foregoing layer in the multilayer structure).
• the Z-axis is directed along the normal to the substrate 1, while X-axis is directed along the direction of the external aligning action 2.
• the Y-axis is directed perpendicular to the plane XZ.
• the direction of the X-axis does not necessarily coincide with the direction of the minor axis (n 3 , k 3 ) of the ellipsoid.
• the minor axis as a rule, is directed perpendicularly to the plane of molecules or flat fragments of molecules.
• the major axis (ni, ki), then, is directed along the primary orientation of the dipole moments of the optical transition of molecules.
• direction of axes (ni, ki), (n 2 , k 2 ) and (n 3 , k 3 ) of the ellipsoids may vary for different areas of the layer (different domains).
• Absorption coefficient k 3 along the axis (n , k ) has the minimum value; and for the multilayer structure used in the capacity of the polarizer it is preferred that it would approach zero.
• the axis (ni, ki) coincides with the direction, along which the absorption coefficient ki is maximum. Also, it should be noted that lowering ki will lead to an increase of k 2 , since this involves reorientation of the dipole moments of optical transition, which is accompanied by some disorientation of molecules in the plane (m, ki - n 2 , k 2 ).
• the necessary anisotropy of absorption and refraction coefficients, as well as orientation of the main axes is possible via imposing certain angular distribution of molecules in the polarizing film on the surface of the substrate. If the distribution function is symmetrical relative to the direction of deposition of the polarizer and the normal to the substrate (Fig. 2), the axes (n b k,) and (n 3 , k 3 ) of ellipse of the absorption coefficient will coincide with those directions, i.e. axes X and Z, while the third axis will be directed perpendicular to them (Y-axis). The axis of minimal absorption then will be the X-axis, while the Y-axis - maximum absorption. In case of asymmetrical angular distribution, the direction of axes may not coincide with the mentioned directions. Thus, via selecting regime of fabricating the anisotropic layer one may obtain crystalline layer with various optical properties.
• the herein invention has been implemented in fabricating a multilayer optical structure, which functions simultaneously as reflecting polarizer and color edge filter in a display.
• the multilayer structure included three layers (Fig. 3): the first layer, along the direction of the incident light, was the optically anisotropic crystalline layer (TCF-R) 3; the second was - Si0 2 4; and the third was the optically anisotropic layer 5 analogous to the first one; the assembly was encased by glass plates 6 from both sides.
• Optically anisotropic layers 3 and 5 were formed out of 7.5% aqueous solution (LLC) of a mixture of cis- and trans- isomers of dibenzoimidazole naphthalenetetracarboxilic acid.
• LLC aqueous solution
• Figures 4 and 5 present spectral dependences of the imaginary and the real parts of the refraction index of the anisotropic layer 3, accordingly.
• Figure 6 presents the spectra of reflection of light by the above-described structure with two different directions of polarization of the incident radiation (R pe r and R par accordingly).
• the herein described optically anisotropic structure is an effective reflecting polarizer of green light (wavelength range 530 - 590 nm) with sharp cutoff in the long- wavelength region of the spectrum.
• the low reflection coefficients in the long- wavelength region ( ⁇ > 600 nm) are due to the decrease of differences between the refraction indexes in different layers of the structure in that region of the spectrum, while in the short- wavelength region ( ⁇ ⁇ 500 nm) it is due to the presence of the of the absorption band in the anisotropic layer.
• this structure serves its functional purpose at incident angles significantly deviating from the normal.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Polarising Elements (AREA)
• Optical Filters (AREA)
• Laminated Bodies (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)

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• 2001
  • 2001-07-10 RU RU2001118989/28A patent/RU2226288C2/ru not_active IP Right Cessation
• 2002
  • 2002-07-10 WO PCT/US2002/023291 patent/WO2003007025A2/en active IP Right Grant
  • 2002-07-10 AU AU2002322582A patent/AU2002322582A1/en not_active Abandoned
  • 2002-07-10 JP JP2003512738A patent/JP4133809B2/ja not_active Expired - Fee Related
  • 2002-07-10 DE DE60204320T patent/DE60204320T2/de not_active Expired - Lifetime
  • 2002-07-10 CN CN028140273A patent/CN100406925C/zh not_active Expired - Fee Related
  • 2002-07-10 AT AT02756580T patent/ATE296454T1/de not_active IP Right Cessation
  • 2002-07-10 EP EP02756580A patent/EP1407296B1/en not_active Expired - Lifetime
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